Mariano RiveraShagging Injury Threatens Career of Yankees Star

5/3/2012 9:40 PM PDT BY TMZ STAFF

Breaking News

NY Yankees pitcher Mariano Rivera -- the greatest closer in baseball history -- could be done for ever after tearing his ACL in a freak injury Thursday night.

Mo twisted his right knee while shagging (baseball term, not the British one) fly balls during batting practice before the Yankees' game in Kansas City. He immediately crumpled to the ground holding the knee ... and had to be removed from the field on a cart.

According to the Yankees, an MRI revealed the torn ACL -- and he'll most likely be out for the rest of the season. 42-year-old Rivera has 608 saves -- the most of all-time -- and is a lock for the Hall of Fame. Even before the injury, Yankees fans were terrified he might retire after this season.

After the game a reporter asked Mariano if he would return next season -- and while fighting tears he responded, "At this point...I don't know. We have to face this first."